Tyre for a vehicle wheel including specific tread patterns

ABSTRACT

A tire for a vehicle wheel includes a carcass structure, a belt structure associated coaxially with the carcass structure, and a tread band extending coaxially around the belt structure. The tread band includes a relief pattern including at least one row of blocks separated by transverse grooves intersecting two circumferential grooves. Each block of the at least one row is essentially delimited by two longitudinal sides in a circumferential direction of the tire and two transverse sides with respect to a predetermined rolling direction of the tire. Each block of the at least one row is formed by two axially-adjacent block portions. The transverse sides of each block portion include at least two successive curvilinear portions shaped differently from each other. The transverse grooves include two branches, each branch including a widened cross-section of substantially-curvilinear shape disposed in an area substantially equidistant from ends of a respective branch.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national-phase entry under 35 U.S.C. § 371 fromInternational Application No. PCT/EP02/01691, filed Feb. 18, 2002, inthe European Patent Office, the contents of which are relied upon andincorporated herein by reference; additionally, Applicants claim theright of priority under 35 U.S.C. § 119(a)-(d) based on patentapplication No. 01830144.0, filed Feb. 28, 2001, in the European PatentOffice; further, Applicants claim the benefit under 35 U.S.C. § 119(e)based on provisional application No. 60/279,431, filed Mar. 29, 2001, inthe U.S. Patent and Trademark Office.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to tyres for motor vehicles, particularlydirectional tyres for use on snow-covered ground.

2. Description of the Related Art

A tyre, in its most general form, comprises: a carcass structureincluding a central crown portion and two axially opposing sidewallsterminating in a pair of beads for securing the tyre to a wheel rim, abelt structure associated coaxially with the carcass structure and atread band extending coaxially around the belt structure.

The tread band is generally moulded with a relief pattern formed by aplurality of longitudinal and transverse grooves which, in combination,give rise to a plurality of blocks distributed according to differenttypes of configurations, for example along a central area extendingacross the equatorial plane and in at least two shoulder areas extendingin axially opposed positions on either side of said central area.

Of particular importance for the purposes of travel on a snow-coveredsurface is the presence, in the blocks, of suitable sipes, in otherwords of a closely spaced set of incisions or small grooves which arecircumferentially distributed and orientated essentially transverselywith respect to the rolling direction. The function of said sipes isessentially to collect and retain the snow in an efficient way, since ithas been shown to be generally convenient to exploit the friction ofsnow on snow to ensure a good grip of a tyre on snow-covered ground.

One type of winter tyre marketed by the Applicant has, in the treadband, a pair of rectilinear circumferential grooves, arrangedsymmetrically with respect to the equatorial plane of the tyre andspaced apart from each other by a distance essentially equal to half ofthe total width of the tread band.

Said circumferential grooves are combined with two sets of transversegrooves, each of which extends with a progressively increasinginclination from the outer edge of the tread band to a point on theequatorial plane.

The transverse grooves of said two sets converge symmetrically on theequatorial plane of the tyre in a predetermined preferred rollingdirection, and have their vertices interleaved with each otheralternately along the perimetric extension of the tread band incorrespondence of the equatorial plane.

In said tread band, the configuration of the transverse grooves is suchas to promote good characteristics of traction because of the mutualconvergence of the grooves in the rolling direction.

Moreover, the circumferential rectilinear grooves enable water to beremoved efficiently from the footprint while the tyre is running on awet surface, thus preventing the onset of the well-known and dangerousphenomenon of aquaplaning.

The traction and the overall behavior in travel on a snow-coveredsurface are improved by the provision of closely spaced sipes in theblocks obtained by the intersection of the longitudinal grooves with thetransverse ones, and by suitable rectilinear grooves, associated withthe transverse grooves, in the space delimited by the twocircumferential grooves, each of said rectilinear grooves extending inthe circumferential direction for a short distance from thecorresponding transverse groove.

Patent EP-773,116, in the name of the same Applicant, discloses a tyrefor snow-covered surfaces, provided with a tread band in which thecircumferential grooves are formed by a sequence of portions orientatedobliquely with respect to the circumferential direction of the tyre.Said oblique portions converge symmetrically towards the equatorialplane according to a direction opposite to the direction of convergenceof the transverse grooves.

Each of the oblique portions of the circumferential grooves extendsbetween two consecutive transverse grooves and delimits respectively theopposing circumferential edges of a centre block and of a shoulderblock.

In this solution, each of the centre and shoulder blocks has a cornerprojecting into the inside of the corresponding circumferential groovewith respect to the opposite corner of the block immediately followingit.

In this situation, the projecting corners of the centre blocks act asteeth which provide the grip on snow in traction, while the projectingcorners of the shoulder blocks produce this effect during braking.

In order to increase the grip on snow, said tyre also has a groove oftrapezoidal shape extending partially between two adjacent blocksbelonging to the same row of centre blocks.

Said groove passes through the transverse groove between the two centreblocks and has an inner circumferential edge and an outercircumferential edge which diverge from each other at angles preferablycomprised from 3° to 15°, in the opposite direction to the rollingdirection.

However, since the tread pattern for a tyre suitable for running onsnow-covered ground has a considerable number of blocks, it inevitablycauses a certain degree of noise when running on dry roads because ofthe successive impacts of the frontal profiles of the blocks on theground.

U.S. Pat. No. 5,759,313 relates to a pneumatic tyre permitting a vehicleto travel excellently both in the on-road condition and in the off-roadcondition without changing its tyres. To achieve such an object, thedocument discloses a tyre, wherein sub-grooves extending at least in thewidthwise direction of the tyre are arranged in the circumferentialdirection thereof at a predetermined pitch in a center portion of atread surface and in shoulder portions thereof on both sides of thecenter portion. Both the width and depth of the sub-grooves in both ofthe shoulder portions are set larger than those of the sub-grooves inthe center portion. A ratio of the area of the sub-grooves in both ofthe shoulder portions to that of the tread surface is set larger than aratio of the area of the sub-grooves in the center portion to that ofthe tread surface.

In considering the cited prior art, the Applicant has perceived thenecessity of providing a tyre for snow-covered ground which cansimultaneously ensure a good grip on said type of ground, a satisfactorynoiseness when running on dry roads, and a high wear-resistance of thetread blocks.

SUMMARY OF THE INVENTION

The Applicant has found that said performances can be achieved by usingprofiles of the frontal sides of adjacent blocks, belonging to the samerow, which are such as to produce, when combined in pairs, grippingmeans with an undulated profile, together with variations of saidprofiles, in order to attenuate the impact of each block on the groundin conditions of rolling on a dry surface.

Therefore, according to a first aspect the present invention concerns awinter tyre for vehicle wheels, comprising: a carcass structureincluding a central crown portion and two axially opposing sidewalls; abelt structure associated coaxially with the carcass structure; and atread band extending coaxially around the belt structure, moulded with arelief pattern which comprises at least one row of blocks separated bytransverse grooves intersecting two lateral circumferential grooves.

Each block of said at least one row of blocks is essentially delimitedby two longitudinal sides in the circumferential direction and by twotransverse sides, also referred to as “frontal profiles” in thefollowing text, respectively one at the front and one at the rear withrespect to a predetermined rolling direction.

The principal characteristics of the tread band according to theinvention are as follows:

-   a) said blocks are formed of two portions axially adjacent with    respect to a longitudinal axis;-   b) said transverse grooves between two circumferentially adjacent    blocks are provided with a widening of the cross section, said    widening having an essentially curvilinear profile in at least one    of said two axially adjacent portions; said widenings of the cross    section between blocks being intended to trap the snow;-   c) the facing frontal profiles of circumferentially adjacent blocks    are formed by at least two successive curvilinear portions which are    different from each other, to form means of attenuating the noise    originating from the contact of the tread band with the ground    during the travel of the tyre.

The term “longitudinal axis” denotes an axis parallel to or possiblyaligned with the equatorial plane of the tyre.

According to a preferred embodiment of the invention, all the blocks ofsaid at least one row of blocks are shaped in the same way.

Preferably, said two curvilinear portions follow each other axially inthe frontal profile of a first portion of a first block with a sequencewhich is the inverse of that present in the corresponding frontalprofile of the other, axially adjacent, portion of said first block.Preferably, said curvilinear portions follow each other axially in thefrontal profile of the two axially adjacent portions of a first blockwith a sequence which is the inverse of that present in the facingfrontal profile of the two corresponding axially adjacent portions of asecond block which is circumferentially adjacent to the first.

Preferably, the frontal profile of each portion of the blocks comprisesa first rectilinear portion followed by said two curvilinear portions.

Preferably, said two curvilinear portions are formed by a firstcurvilinear portion which is concave towards the inside of the block andby a second curvilinear portion having a curvature opposite to that ofthe first portion.

Preferably, the axially adjacent portions of the blocks of said at leastone row of blocks are respectively contained in two axially adjacentrows of imaginary parallelograms in which:

-   the longitudinal sides of said parallelograms are parallel to the    equatorial plane of the tyre and partially coincide with the    longitudinal sides of the blocks;-   the transverse sides of the parallelograms of each row are parallel    to each other, converge towards the equatorial plane and partially    coincide with the transverse sides of the blocks;-   the ratio between the minor diagonal and the major diagonal of said    parallelograms is preferably in the range from 0.50 to 0.70.

Preferably, each of the two adjacent portions of said blocks isessentially in the shape of an irregular rhombus, with the majordiagonal inclined with respect to the equatorial plane at an angle inthe range from 25° to 55°.

Preferably, said two portions of each block are joined together alongthe adjacent longitudinal side.

Preferably, at least one of the two frontal profiles of each block has aconcavity located in a central position, in other words extendingessentially across the equatorial plane of the tyre.

Said concavity advantageously forms a further means by which the treadband according to the invention can trap snow and, therefore, as statedabove, provide an grip of the tyre when running on snow-covered ground.

In a preferred embodiment of the invention, the tread band comprises acentre row of blocks, located across the equatorial plane and containedbetween two circumferential grooves, and two lateral rows of blocks,formed between said two circumferential grooves and the edges of thetread band.

Each block of the centre row, as mentioned above, comprises theaforesaid two axially-adjacent portions joined together incorrespondence of a longitudinal axis passing through the centre of theblock.

The blocks of said lateral rows, also called shoulder blocks, can havevarious shapes. Said shapes can be identical to those of the blocks ofthe centre row or can have polygonal shapes different from those of thecentre blocks.

Preferably, the tread pattern present on one side of the equatorialplane is a mirror image of that present on the other side.

In a preferred embodiment of the invention, curvilinear profiles of thecentre blocks and of the lateral blocks face each other and are opposedto each other along the circumferential grooves. Said opposingcurvilinear profiles cause the formation of a widening of thecircumferential groove which can trap the snow more efficiently, withthe advantages described above.

Preferably, each of the centre and shoulder blocks has a plurality ofsipes in it.

Further characteristics and advantages will be made clearer by thefollowing description of an example of a preferred embodiment of a tyreaccording to the invention, provided for guidance and withoutrestrictive intent, with reference to the attached drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a partial cross-sectional view of a tyre according to theinvention;

FIG. 2 shows a development, in plan view from the top, of the tread bandof the tyre of FIG. 1;

FIG. 3 shows an enlargement of a portion of FIG. 2;

FIG. 4 shows some details of a block illustrated in the partial planview of FIG. 2;

FIG. 5 shows a comparison between portions of the profile of a blockaccording to the invention and corresponding portions of the profile ofa known block.

DETAILED DESCRIPTION OF THE EMBODIMENTS

With reference to FIG. 1, reference sign 1 indicates in a general way atyre for motor vehicles according to the invention, for example a tyreof the 155/70 R13 size.

The tyre 1 comprises a carcass structure 2, including a central crownportion 3 and two sidewalls 4, 5, said carcass structure 2 beingprovided with a reinforcing ply 2 a whose opposite ends 2 b, 2 c arewound around corresponding bead cores 6, 7.

An elastomeric filler 8 is applied to the radially outer perimetric edgeof the bead cores 6, 7 which are located at the radially inner edges ofsaid sidewalls 4, 5, said elastomeric filler being positioned in thespace formed between the reinforcing ply 2 a and the corresponding ends2 b, 2 c of said reinforcing ply 2 a.

As is known, the opposing areas of the tyre 1, each comprising a beadcore 6, 7 and the filler 8, form what are known as beads, indicated as awhole by 9 and 10, intended to secure the tyre 1 on a correspondingmounting rim 11 of the wheel of a vehicle.

A belt structure 12, comprising one or more reinforcing strips 13 madefrom textile or metal cords incorporated in a specified mixture, isassociated coaxially with the aforesaid carcass structure 2.

A tread band 14, in the thickness of which a pattern shown in moredetail in FIG. 2 is cut, is applied in a known way to the belt structure12.

The tread band 14 according to the invention is particularly suitablefor snow-covered surfaces.

As shown in FIG. 2, the tread band 14 comprises a central row 15 ofblocks axially delimited between two circumferential grooves 16, 17.

The centre row 15 comprises blocks, each of which is formed by twoportions 18, 19 which are axially adjacent to each other on alongitudinal axis which, in the illustrated embodiment, belongs to theequatorial plane Y-Y of the tyre.

Said tread band 14 also comprises two rows of shoulder blocks 20, 21,located on opposite sides of the centre row 15. Additionally, the blocksof the shoulder rows 20, 21 are delimited externally in the axialdirection by the shoulder disconnection grooves O, O′ of the tread band14.

The transverse grooves of the centre row 15 have two branches 22, 23whose mid-line axes m-m′ converge towards the equatorial plane with aninclination lying in the rolling direction of the tyre which isindicated by the arrow H in FIG. 2.

Said transverse grooves of the centre row 15 intersect thecircumferential grooves 16, 17 and continue to form the transversegrooves 24 and 25 of the shoulder rows 20 and 21 respectively.

Preferably, the circumferential grooves 16, 17 have mid-line axesparallel to the equatorial plane. Preferably, said grooves have a depthin the range from 6 to 12 mm. The width of the circumferential grooves16, 17 is preferably in the range from 4 to 8 mm.

Preferably, the transverse grooves 22-25 have a depth in the range from4 to 12 mm. Preferably, they have a width in the range from 3 to 6 mm.

Preferably, both the transverse and the circumferential grooves have thesame depth, for example of 8 mm.

As clearly shown in FIG. 2, the portion of the tread band 14 located onthe left of the equatorial plane Y-Y is a mirror image of the partlocated on the right of said equatorial plane.

Each block of the tread band according to the invention comprises twolongitudinal sides and two transverse sides, respectively the front sideand the rear side, with respect to the direction of travel.

Each block of the centre row 15 is formed by at least two portions 18,19 which are axially adjacent with respect to a longitudinal axis; eachportion has an irregular rhomboidal shape.

In greater detail, as shown in FIG. 3, each portion 18, 19 of a block ofthe centre row 15 is contained in a regular parallelogram formed by apair of longitudinal sides “a”, “b”, parallel to the equatorial plane,and by a pair of transverse sides “c”, “d”, inclined at equal angleswith respect to the equatorial plane. Said parallelogram has a pair ofdiagonals l₁, l₂.

The two parallelograms delimiting each block of the centre row have incommon the side “b” aligned along the equatorial plane.

Each portion 18, 19 of the block 15 departs from the aforesaidparallelogram in the following ways:

-   the axially outer longitudinal side of each portion of the block is    aligned with the outer side “a” of the parallelogram and its length    is lower than “a”. Preferably, the length of the axially outer    longitudinal side of each portion of the block does not exceed 75%    of the length of “a”;-   the axially-inner longitudinal side of each portion of the block is    aligned with the side “b” of the parallelogram and has a length    substantially equal to that of the axially-outer longitudinal side;-   the transverse sides of each portion of the block have a portion of    predetermined length, preferably not exceeding 35% of the length of    “c”, in common with the transverse sides of the parallelogram;-   the maximum extension of each portion of the block is equal to the    longer diagonal l₁ of the parallelogram; preferably, said diagonal    l₁ is inclined with respect to the equatorial plane at an angle δ    whose value is in the range from 25° to 55°; preferably, said value    does not exceed 45°;-   the maximum transverse dimension of each portion of the block is    smaller than the length of the shorter diagonal 12 of the    parallelogram. Preferably, said maximum transverse dimension of each    portion of the block is not greater than 75% of l₂;-   the overall shape of each portion of block is a sharp ovoid shape,    similar to that of a leaf, inscribed in a parallelogram in which the    ratio l₂/l₁ between the smaller diagonal and the longer diagonal is    preferably in the range from 0.50 to 0.70.

It was stated above that the axially inner longitudinal sides of the twoportions of block are aligned along the central longitudinal axis of theblock (in the described example they are aligned on the equatorialplane). However, it should be noted that, for the purposes of thepresent invention, the block 15 is considered to be a single block bothwhen it comprises two separate axially adjacent portions separated by asipe and when, alternatively, block 15 is formed by the aforesaid twoseparate portions joined together along their axially inner longitudinalside which is common to both of said portions.

In the case of separate portions, the depth of the separating sipe ispreferably in the range from 4 to 12 mm. Preferably, the width of saidsipe does not exceed 2 mm.

In particular, it should be noted that, regardless of the configurationused, the two axially adjacent portions of each centre block, joinedtogether in this way, form, at least on one of the two frontal profilesof the block, a concavity 26 defined below in greater detail.

Advantageously, the shape and dimensions of the centre block 15 help toprovide the block with sufficient deformability to give it advantageousproperties of adaptation to particularly rough grounds.

It should be noted that the frontal profiles of both the adjacentportions of each centre block have a particular configuration whichcomprises at least three distinct portions, all three being shapeddifferently from each other.

For example, the enlargement of FIG. 3 shows that the frontal profile ofeach portion 18, 19 of the centre block comprises a first rectilinearportion 27 and two successive curvilinear portions 28, 29, one beingconcave and the other convex towards the outside.

Preferably, said curvilinear portions are parabolic and/or circulararcs.

As shown in FIGS. 3 and 4, the first rectilinear portion 27 is inclinedwith respect to a plane perpendicular to the equatorial plane at anangle β whose value is in the range from 20° to 35°.

Preferably, the first and the second curvilinear portions are bothshaped in the form of successive portions of circular arcs.

More precisely, the first curvilinear portion 28 comprises two circulararcs, having a first and second radius r₁, r₂, while the secondcurvilinear portion 29 comprises a third circular arc with a radius r₃linked to said second circular arc by a fourth circular arc with aradius r₄.

Preferably, the configuration of the frontal profile of a portion of theblock has the following additional characteristics:

-   the ratio between the radii r₁ and r₂ of the first and second    circular arcs is in the range from 1 to 6;-   the ratio between the radii r₃ and r₂ of the third and second    circular arcs is in the range from 1 to 4;-   the link radius r₄ has the smallest value of all the radii mentioned    above;-   the distance “q” between the first rectilinear portion and the    parallel line, tangent to the second circular arc at the point R of    maximum extension of the cavity formed by said curvilinear portion    28, measured perpendicularly to said rectilinear portion, is in the    range from 1.5 to 3 mm.

It can be seen in FIGS. 2 and 3 that, in a given centre block, the threedifferent portions 27, 28, 29, for example the portions of the frontalprofile in the front of the portion 19 on the right of the equatorialplane, have a sequence which is the inverse, in the axial direction, ofthat of the three similar portions of the frontal profile in the rear ofthe corresponding circumferentially adjacent portion of block.

The same geometrical characteristic is repeated for the configuration ofthe portion 18 of the block on the left of the equatorial plane.

Said characteristic makes it possible to form a cross section widening30 of curvilinear shape in each branch 22, 23 of the transverse grooveof the centre row.

Preferably, said widening is circular in shape.

Preferably, said widening is located in an area substantiallyequidistant from the ends of each branch of said transverse groove.

The Applicant has found that the curvilinear shape of the cross sectionwidening 30 advantageously maintains a sufficient resistance to bothtearing and fatigue in the elastomeric material of the block.

Furthermore, said cross section widening 30 advantageously forms agripping means which is particularly suitable for trapping snow, asindicated by the hatching in FIG. 2.

Advantageously, each transverse groove of the centre row of the treadband has a further means of trapping snow formed by the aforesaidconcavity 26 obtained in the centre of at least one of the two frontalprofiles of each block.

Said concavity 26 preferably comprises a closed end with a linear orcurvilinear profile, and side walls which are parallel to, or inclinedwith respect to, the equatorial plane. The side walls of said cavity 26form the axially inner terminal portions of the frontal profiles of thetwo axially adjacent portions 18, 19 of each block.

The minimum transverse dimension of said cavity 26, measuredperpendicularly to the equatorial plane, is preferably in the range from7 to 15 mm.

Preferably, the transverse groove between two circumferentially adjacentblocks of the centre row has its point of maximum width, measuredparallel to the equatorial plane, lying on the axis of the concavity 26.

Preferably, the ratio between the width of the transverse groove, at thecross section widening 30, and the width of the cavity 26 is in therange from 0.30 to 1. More preferably, said ratio is in the range from0.40 to 0.90.

The blocks 31 of the lateral rows 20, 21 can have various shapes,provided that they are compatible with the shapes of the blocks of thecentre row.

For the purposes of the invention, the most convenient shape of saidblocks of the lateral rows is that shown in FIG. 2.

In the embodiment shown in FIG. 2, each block 31 of the shoulder rows20, 21 is delimited by longitudinal sides 32, 33 parallel to theequatorial plane Y-Y, by transverse sides 34, 35 with a curvilinearprofile, and by a curvilinear portion 36 linking the axially innerlongitudinal side with one of the transverse sides.

In the example shown in FIG. 2, the curvilinear portion 36 forms a linkwith the rear transverse side 34.

The shoulder blocks 31 follow each other circumferentially with apredetermined pitch “p”; in a tyre of the aforesaid measure, said valueis preferably in the range from 20 to 35 mm.

The centre blocks and the adjacent shoulder blocks 31 arecircumferentially staggered with respect to each other by a distancepreferably equal to one half of the pitch.

Preferably, as shown in the enlargement in FIG. 3, said staggering isproduced in such a way that the curvilinear link 36 between a transverseside and a longitudinal side of a shoulder block 31 faces thecurvilinear link 36′ formed between a longitudinal side and a transverseside of the centre block.

In FIG. 3, “K” indicates the minimum distance between said circularlinks 36, 36′.

The design of the centre blocks and of the shoulder blocks is obtainedwith curvilinear links which make the profiles of said blocks to departfrom those of a rhomboidal shape which contain them.

Essentially, as indicated by the hatching in FIG. 3, the aforesaid links36, 36′ remove a quantity of elastomeric material corresponding to theareas 37, 38 from the centre and shoulder blocks.

Advantageously, said design and arrangement of the blocks provides alocalized widening of the lateral circumferential grooves 16, 17 and aconsequent improvement in the trapping of snow between the blocks, asschematically shown by hatching in the area 39 of FIG. 3.

In order to optimize the grip of the tread band according to theinvention on snow-covered ground, each of the centre and shoulder blocksis provided with a plurality of notches, known to those skilled in theart as “sipes”.

Preferably, the sipes of the axially adjacent portions 18, 19 of theblocks of the centre row 15 are parallel to each other in each portion,with direction different from the mid-line axes of the correspondingbranches 22, 23 of the transverse grooves.

In greater detail, the axially adjacent portions 18, 19 of the centreblocks comprise a plurality of linear sipes 40, parallel to each otherin each portion and inclined with respect to the equatorial plane atangles preferably in the range from 15° to 50°.

Preferably, the sipes of the blocks 31 of the shoulder rows 20, 21 havea different profile from that of the corresponding transverse grooves24, 25.

More particularly, each of the shoulder blocks 31 comprises a pluralityof sipes 41 generated by a sequence of three consecutive portions in theshape of a zigzag, with the intermediate portion inclined in theopposite direction to that of the sipes 40 provided in the adjacentportions of the blocks of the centre row 15.

The angle of inclination of the intermediate portions of the sipes 41with respect to the equatorial plane Y-Y is preferably in the range from40° to 60°.

The Applicant has found that the orientations of the sipes and of thetransverse grooves improve the traction of the tyre according to theinvention on snow and do not have an adverse effect on tyre quietnesswhen running on a dry surface.

In order to optimize the grip of the tread band on a snow-coveredsurface, both the shoulder blocks and the centre blocks can comprisenotches 42 located in correspondence of the axially outer longitudinalsides of the shoulder blocks, for example in the proximity of the endsof the sipes of said shoulder blocks.

Preferably, all the shoulder blocks comprise said notches in order totrap snow at the end of each shoulder block.

Said notches are distributed in a substantially uniform way with anorientation which is preferably perpendicular to the equatorial plane ofthe tyre.

Preferably, the notches 42 have a depth which is lower than the depth ofthe sipes.

Preferably, the notches 42 have a width which is greater than the widthof the sipes.

In an example of embodiment, the notches 42 have a width and a depth of2 mm. The ratio between the depth of the notches and that of the sipesis 0.25.

Additionally, in order to obtain better traction of the tyre onsnow-covered surfaces, the ratio (FIG. 2) between the axial width“L_(c)” of the row of centre blocks 15 and the total width “W” of thetread band, measured between the edges of the tread, is preferably notgreater than 0.33.

In a further embodiment of the invention, the blocks 31 of the shoulderrow 21 are symmetrically arranged with respect to the blocks 31 of theshoulder row 22; in other words they have an orientation which isrotated through 180° in the plane in which they lie with respect to theorientation of the mirror symmetry arrangement.

The tyre according to the invention has served to decrease the noise ofrunning on a dry surface.

The Applicant considers that one of the factors which may havecontributed to the achievement of improved noiseness of the tyreaccording to the invention may be the particular profile of thetransverse sides of the centre blocks.

To provide a better understanding of the possible improvements in termsof quietness, FIG. 5 shows the frontal profile of a conventional block,having a rectilinear profile N, and the frontal profile of a blockaccording to the invention, in the condition in which successive pointsof the profiles of said blocks touch the ground during the progressiveadvance of the tyre in the rolling direction H.

The progressive advance of the tyre on the ground is represented by thelines 101-108, which are all located at equal distance from each other.

As shown in FIG. 5, in the case of a block having a profile N of therectilinear type along its whole transverse extension, portions ofidentical shape and length progressively come into contact with theground. Therefore, the frontal profiles in the front of the block strikethe ground in succession at a single specific frequency which is asource of noise.

In the case of the invention, on the other hand, it may be noted thatthe contact with the ground of a portion 18, 19 of the block involvesportions of identical inclination and length (for example the portionsAB and BC), followed by a portion CD, which differs in both inclinationand length from the preceding portions, by a portion DE which has adifferent inclination from, and is longer than, the preceding ones,followed by a portion EF with a configuration and linear dimension whichis greater than the preceding ones and with a profile which iscompletely different from the preceding ones, and then by a portion FGwhich is different from and shorter than the preceding one.

Therefore, the Applicant considers it reasonable to assert that thecontact with the ground of the transverse side of a block according tothe invention does not give rise to a repetitive phenomenon such as thatfound in the case of a rectilinear profile N according to the prior art.

This could, therefore, be responsible for the improved quietness whichhas been found in the tread band according to the invention.

The tread band according to the invention can be made with a number ofrows of blocks greater than that described above.

For example, in a further embodiment which is not illustrated, the treadband can comprise, in addition to the central row of blocks 15 and tothe two lateral shoulder rows 20, 21 (as shown in FIG. 2), two furtherintermediate rows of blocks, each interposed between the centre row andthe shoulder row.

Additionally, the design and arrangement of the blocks of theintermediate rows can be such as to permit the aforesaid localizedwidening of the circumferential grooves, resulting in improved tractionof the tyre on a snow-covered surface, the whole as shown schematicallyin FIG. 3 with reference to the hatched area 39.

It should also be noted that the blocks of the intermediate rows canhave configurations identical to those of the centre row, or could havepolygonal profiles different from those described.

1. A tyre for a vehicle wheel, the tyre being configured to be providedon a contact surface, the tyre comprising: a carcass structure; a beltstructure associated coaxially with the carcass structure; and a treadband extending coaxially around the belt structure; wherein the carcassstructure comprises a central crown portion and two axially-opposedsidewalls, wherein the tread band comprises a relief pattern comprisingat least one row of blocks separated by transverse grooves intersectingtwo circumferential grooves, wherein each block of the at least one rowis essentially delimited by two longitudinal sides in a circumferentialdirection of the tyre, wherein each block of the at least one row isessentially delimited by two transverse sides, a front side and a rearside with respect to a predetermined rolling direction of the tyre,wherein each block of the at least one row is formed by two blockportions, wherein the two block portions of each block are mirror imagesof each other, wherein the two block portions are axially adjacent toeach other, wherein each of the transverse sides of each block portioncomprise at least two successive curvilinear portions shaped differentlyfrom each other, wherein the transverse grooves comprise two branches,wherein each branch comprises a widened branch cross-section ofsubstantially-curvilinear shape wherein a junction of the two branchesdefines a widened junction cross-section, and wherein each widenedbranch cross-section is disposed in an area substantially equidistantfrom ends of a respective branch, the widened junction cross-sectionbeing wider than the widened branch cross-section.
 2. The tyre of claim1, wherein each block of the at least one row comprises an identicalshape.
 3. The tyre of claim 1, wherein the at least two successivecurvilinear portions comprise a first curvilinear portion, concavetoward an inside of a respective block portion, and a second curvilinearportion, with a curvature opposite to that of the first curvilinearportion.
 4. The tyre of claim 1, wherein a transverse edge profile ofeach block portion comprises two successive curvilinear portions whoseshape lean inverse of two successive curvilinear portions of a facingtransverse edge profile of a circumferentially-adjacent block portion.5. The tyre of claim 1, wherein an edge profile of each of thetransverse sides comprises a rectilinear portion followed by the atleast two successive curvilinear portions.
 6. The tyre of claim 5,wherein each block portion is contained in one of two axially-adjacentrows of rhombuses, and wherein each rectilinear portion is inclined atan angle greater than or equal to 55° and less than or equal to 70° withrespect to an equatorial plane of the tyre.
 7. The tyre of claim 5,wherein the at least two successive curvilinear portions compile a firstcurvilinear portion, concave toward an inside of a respective blockportion, and a second curvilinear portion, with a curvature opposite tothat of the first curvilinear portion.
 8. The tyre of claim 7, whereinthe first curvilinear portion is a parabolic arc, and wherein the secondcurvilinear portion is also a parabolic arc.
 9. The tyre of claim 5,wherein the at least two successive curvilinear portions comprise afirst curvilinear portion and a second curvilinear portion, wherein thefirst curvilinear portion comprises a first circular arc and a secondcircular arc, wherein the second curvilinear portion comprises a thirdcircular arc, wherein a radius of the first circular arc is greater thana radius of the second circular arc, and wherein a radius of the thirdcircular arc is greater than the radius of the second circular arc. 10.The tyre of claim 9, wherein the first curvilinear portion forms aconcavity, and wherein a perpendicular distance between the rectilinearportion and a line both parallel to the rectilinear portion and tangentto the concavity is greater than or equal to 1.5 mm and less than orequal to 3 mm.
 11. The tyre of claim 9, wherein a ratio of the radius ofthe first circular arc to the radius of the second circular arc isgreater than or equal to 1 and less than or equal to
 6. 12. The tyre ofclaim 9, wherein a ratio of the radius of the third circular arc to theradius of the second circular arc is greater than or equal to 1 and lessthan or equal to
 4. 13. The tyre of claim 9, wherein the second circulararc and the third circular arc are linked together by a fourth circulararc, wherein a radius of the fourth circular arc is less than the radiusof the first circular arc, wherein the radius of the fourth circular arcis less than the radius of the second circular arc, and wherein theradius of the fourth circular arc is less than the radius of the thirdcircular arc.
 14. The tyre of claim 1, wherein the two block portions ofeach block are symmetrical.
 15. The tyre of claim 1, wherein the twoblock portions of each block are joined together.
 16. The tyre of claim1, wherein the two block portions of each block are separated by a sipe.17. The tyre of claim 1, wherein a central longitudinal axis of eachblock is aligned on an equatorial plane of the tyre.
 18. The tyre ofclaim 1, wherein the block portions are essentially rhombus-shaped. 19.The tyre of claim 18, wherein a longer diagonal of the essentiallyrhombus-shaped block portions forms an angle greater than or equal to25° and less than or equal to 55° with respect to an equatorial plane ofthe tyre.
 20. The tyre of claim 18, wherein longer diagonals ofaxially-adjacent block portions converge symmetrically with respect to acentral longitudinal axis of each block.
 21. The tyre of claim 1,wherein the block portions are essentially rhomboid-shaped.
 22. The tyreof claim 21, wherein a longer diagonal of the essentiallyrhomboid-shaped block portions forms an angle greater than or equal to25° and less than or equal to 55° with respect to an equatorial plane ofthe tyre.
 23. The tyre of claim 21, wherein longer diagonals ofaxially-adjacent block portions converge symmetrically with respect to acentral longitudinal axis of each block.
 24. The tyre of claim 1,wherein axially-outer longitudinal sides of each block portion areparallel to an equatorial plane of the tyre.
 25. The tyre of claim 1,wherein each block portion is contained in one of two axially-adjacentrows of parallelograms, wherein axially-inner longitudinal sides of theparallelograms are parallel to an equatorial plane of the tyre, whereinaxially-outer longitudinal sides of the parallelograms are parallel tothe equatorial plane of the tyre, wherein, in each axially-adjacent rowof parallelograms, transverse sides of the parallelograms are parallelto each other, wherein transverse sides of axially-adjacentparallelograms converge toward the equatorial plane of the tyre, andwherein the transverse sides of the parallelograms partially coincidewith transverse edge profiles of the block portions.
 26. The tyre ofclaim 25, wherein, for each parallelogram, a ratio of a length of ashorter diagonal to a length of a longer diagonal is greater than orequal to 0.5 and less than or equal to 0.7.
 27. The tyre of claim 1,wherein each transverse groove comprises a concavity in at least onetransverse edge profile of two respective circumferentially-adjacentblocks, and wherein each concavity is disposed in a center of therespective transverse groove.
 28. The tyre of claim 1, wherein eachtransverse groove comprises a concavity in at least one transverse edgeprofile of two respective circumferentially-adjacent blocks, and whereineach concavity straddles an equatorial plane of the tyre.
 29. The tyreof claim 1, further comprising two rows of shoulder blocks, wherein afirst row of shoulder blocks is disposed between a first circumferentialgroove and a first edge of the tread band, wherein a second row ofshoulder blocks is disposed between a second circumferential groove anda second edge of the tread band, wherein the shoulder blocks of thefirst row are separated from each other by first lateral transversegrooves, and wherein the shoulder blocks of the second row are separatedfrom each other by second lateral transverse grooves.
 30. The tyre ofclaim 29, wherein the blocks of the at least one row and the shoulderrows comprise sipes.
 31. The tyre of claim 30, wherein each sipe in ablock portion is parallel to each other sipe in the block portion. 32.The tyre of claim 30, wherein, on a first side of an equatorial plane ofthe tyre, the sipes in each block portion are parallel to each other,and wherein, on a second side of the equatorial plane of the tyre, thesipes in each block portion are parallel to each other.
 33. The tyre ofclaim 30, wherein, with respect to an equatorial plane of the tyre, thesipes of a first block portion are inclined in an opposite direction tothe sipes of an axially-adjacent second block portion.
 34. The tyre ofclaim 30, wherein, with respect to an equatorial plane of the tyre, thesipes of each block portion are inclined in an opposite direction to thetransverse sides of the block portion.
 35. The tyre of claim 30, whereinthe blocks of the shoulder rows comprise zigzag-shaped sipes.
 36. Thetyre of claim 30, wherein the sipes of the block portions and the sipesof the blocks of the shoulder rows comprise essentially a same depth.37. The tyre of claim 30, wherein the sipes of the block portions, thesipes of the blocks of the shoulder rows, the circumferential grooves,and the transverse grooves comprise essentially a same depth.
 38. Thetyre of claim 30, further comprising notches; wherein depths of thenotches are smaller than depths of the sipes.
 39. The tyre of claim 38,wherein a ratio of the depths of the notches to the depths of the sipesis 0.25.
 40. The tyre of claim 29, wherein, with respect to anequatorial plane of the tyre, the blocks of the first and secondshoulder rows are arranged symmetrically.
 41. The tyre of claim 29,wherein a shape of the blocks of the first shoulder row is a mirrorimage of a shape of the blocks of the second shoulder row.
 42. The tyreof claim 29, wherein each block of the shoulder rows is delimited bylongitudinal sides that are parallel to an equatorial plane of the tyre,wherein each block of the shoulder rows is delimited by two transversesides with curvilinear profiles, and wherein each block of the shoulderrows is delimited by a curvilinear linking profile between anaxially-inner longitudinal side and a rear transverse side with respectto the predetermined rolling direction of the tyre.
 43. The tyre ofclaim 29, wherein curvilinear profiles of the at least one row of blocksand the first row of shoulder blocks are arranged opposite each otheralong the first circumferential groove, producing a widening of thefirst circumferential groove, and wherein curvilinear profiles of the atleast one row of blocks and the second row of shoulder blocks arearranged opposite each other along the second circumferential groove,producing a widening of the second circumferential groove.
 44. The tyreof claim 1, wherein a ratio of an axial width of the at least one row ofblocks to a width of the tread band measured between edges of the treadband is less than or equal to 0.33.
 45. The tyre of claim 1, wherein thetread band comprises a relief pattern comprising a row of center blocks,two rows of intermediate blocks, and two rows of shoulder blocks,wherein a first row of shoulder blocks is disposed between a first edgeof the tread and a first circumferential groove, wherein a first row ofintermediate blocks is disposed between the first circumferential grooveand a second circumferential groove, wherein the row of center blocks isdisposed between the second circumferential groove and a thirdcircumferential groove, wherein a second row of intermediate blocks isdisposed between the third circumferential groove and a fourthcircumferential groove, wherein a second row of shoulder blocks isdisposed between the fourth circumferential groove and a second edge ofthe tread, wherein the shoulder blocks of the first row are separatedfrom each other by first transverse grooves, wherein the intermediateblocks of the first row are separated from each other by secondtransverse grooves, wherein the block portions are separated from eachother by third transverse grooves, wherein the intermediate blocks ofthe second row are separated from each other by fourth transversegrooves, and wherein the shoulder blocks of the second row are separatedfrom each other by fifth transverse grooves.
 46. The tyre of claim 45,wherein, in a row of intermediate blocks, each block comprises anidentical shape.